Vaginal myeloperoxidase and flora in the pig-tailed macaque

Myeloperoxidase (MPO) is an enzyme in neutrophils and monocytes which reacts with H2O2 and chloride to kill microbes after phagocytosis. Instillation of MPO into the vagina may augment vaginal defenses against sexually transmitted diseases, since the normal vaginal flora is characterized by the presence of H2O2-producing lactobacilli. We assessed the menstrual cycle stage, vaginal flora, pH, macroscopic appearance, and endogenous MPO in the adult female pig-tailed macaque (Macaca nemestrina) at baseline (n = 26; 60 observations) and at 0, 4, and 24 hours in untreated animals (n = 6) or in animals treated with intravaginal MPO gel at time 0 (n = 5). Baseline MPO levels were highly variable, and there was no detectable effect of cycle stage. In untreated animals, there was no significant effect of vaginal swab collection on vaginal flora or MPO levels. MPO treatment did not reduce vaginal H2O2-producing organisms, and vaginal MPO levels tended to increase at 4 hours in treated animals. Vaginal/cervical colposcopic changes were not detected in either group.